1. Field of the Invention
The present invention relates to a filter device for removing impurities contained in liquid, and so on.
2. Description of the Related Art
There has been conventionally used a filter device by the use of a bag filter for the purpose of cleaning of liquid or the disposal of waste liquid.
A filter device in the conventional art will be explained in reference to FIGS. 18 to 20. FIG. 18 is a cross-sectional view schematically showing the configuration of a bag filter in the conventional art; and FIGS. 19 and 20 are diagrams illustrating the flow of a filter system by the use of the bag filter in the conventional art.
A bag filter 100 in the conventional art comprises a filter bag (bag-like filter) 101, a mesh-like bag filter bucket 102 for protecting the filter bag 101 and a filter presser 105 for positioning the filter bag 101. These are housed inside of a filter housing 108 (see FIG. 18).
Furthermore, the bag filter 100 comprises a cover 106 for the filter housing 108 and a clamp 107 for fixing the bag filter 100 at a predetermined position.
At the filter housing 108 are formed an inlet 103 for introducing liquid to be filtered into the filter housing and an outlet 104 for introducing filtered liquid (i.e., purified liquid) out of the filter housing. The bag filter 100 is used in the state in which the inlet 103 is located above while the outlet 104 is located below.
A filter system for performing specific gravity difference separation by the use of the bag filter 100 will be explained below in reference to FIGS. 19 and 20. Incidentally, the specific gravity difference separation signifies separating things of a specific gravity smaller than that of constituent liquid of purified liquid (liquid to be filtered) such as floating oil (for example, oil with respect to water).
In the filter system illustrated in FIG. 19, a pump 120 is disposed downstream of a cleaning tank 110. The bag filter 100 is disposed downstream of the pump 120. Moreover, a coalescer 130 is disposed downstream of the bag filter 100.
Cleaning liquid as liquid to be filtered contained inside of the cleaning tank 110 flows in a direction indicated by an arrow K by the pump 120. The cleaning liquid further flows in a direction indicated by an arrow L, to be filtered by the bag filter 100. Here, impurities contained in the cleaning liquid are separated, and then, the filtered liquid flows in a direction indicated by an arrow M.
Oil, which is small in specific gravity out of the filtered liquid, is separated by the effect of the specific gravity difference separation by the coalescer 130. The separated oil is discharged in a direction indicated by an arrow N.
The liquid, from which the impurities are separated and the oil is separated and removed, is allowed to flow in a direction indicated by an arrow O, and then, returns to the cleaning tank 110.
In a filter system illustrated in FIG. 20, a hollow fiber membrane module (UF: ultrafiltration) 140 is further disposed downstream of a coalescer 130, unlike the system illustrated in FIG. 19. With this system, the liquid after the oil is discharged is further cross-flow filtered by hollow fiber membrane module 140. Consequently, finer impurities can be removed. Here, the liquid which is not filtered by the hollow fiber membrane module 140 returns upstream of a pump 120.
The above-described bag filter 100 is used such that the opening formed at the bag-like filter bag 101 is located above. And, the liquid to be filtered is allowed to flow in through the inlet 103 located above, and then, the filtered liquid is allowed to be flow out through the outlet 104 located below. In this manner, the filtration is performed. Therefore, the impurities to be filtered are liable to stay at the lower portion of the bag-like filter. In this way, if the impurities are deposited at the lower portion of the filter, a filtration effective area is reduced. This shortens the lifetime of the filter.
Moreover, in the above-described bag filter 100, the liquid flowing into the bag filter is agitated by the flow. As a consequence, the bag filter 100 cannot perform the specific gravity difference separation. Thus, in order to perform the specific gravity difference separation, a special tank for recovering the floating oil or the like (such as the above-described coalescer 130) is required independently.